1. Field of the Invention
The present invention relates to a combustor for a gas turbine engine, and, more particularly, to a thermally protected venturi for the combustor dome of a gas turbine engine.
2. Description of Related Art
In the design of gas turbine engines, it has become important to not only provide a combustor apparatus which is efficient, but one which minimizes emissions as well. One manner of diminishing emissions involves the injection of water into the combustor to reduce the temperature therein, oftentimes through the nozzle circuit utilized for supplying fuel.
In one such combustor design, the nozzle is spaced a distance from the dome area, rather than immediately adjacent thereto. This configuration is utilized to prevent carbon clusters from forming in the nozzle resulting from close proximity to the harsh combustion zone.
Although water injection has been effective in combating emissions, such injection in the aforementioned design has had the undesirable effect of causing metal distress and erosion to the inner diameter of the venturi carrying the injected water to the combustion zone. Since prior art combustors have normally been configured to have the fuel nozzle approximately even with the end of the swirl cup or adjacent to the combustion zone (e.g., U.S. Pat. No. 4,934,145 to Zeisser), this problem is a relatively recent and peculiar occurrence. The cause of thermal distress and erosion to the venturi stems from relatively cold water impinging onto the relatively hot metal surface of the venturi. Water is more punitive than other fluids passing through the venturi because it has a higher coefficient of convective heat transfer and, all else being equal, causes higher thermal stress. This explains why water causes problems, whereas liquid fuel and steam does not.
Accordingly, a primary objective of the present invention is to provide a thermally protected venturi for a combustor which prevents water injected to reduce emissions from causing metal distress and erosion to the inner diameter of the venturi.
Another objective of the present invention is to provide a venturi with a reduced temperature gradient for handling water impinging thereon, thereby reducing exposure to thermal stress and erosion.
Yet another objective of the present invention is to reduce the momentum in which water is swirled in the venturi to lower its impingement intensity and resulting coefficient of convective cooling.
These objectives and other features of the present invention will become more readily apparent upon reference to the following description when taken in conjunction with the following drawing.